1. Field of the Invention
The present invention relates to moisture sensors for use in irrigation. More specifically, the present invention relates to capacitance-based moisture sensors.
2. Discussion of the Related Art
Generally, in irrigation systems utilizing a moisture sensor, a moisture sensor is placed in the ground that outputs information about a moisture level of surrounding soil to an irrigation controller in a separate location. The irrigation controller is typically coupled to and controls multiple valves that control water flow to one or more sprinkler devices. The irrigation controller processes the information received from the sensor and modifies a watering cycle for one or more valves based upon the moisture sensor measurements, e.g., when the soil reaches a given moisture content, further irrigation is prevented. In many irrigation systems, the controller uses a single moisture sensor for all of the zones (a zone generally defined as an area watered by a given valve) within the irrigation system. This is a problem when, for example, different zones have different soil types or are exposed to a different amount of sunlight or weather conditions than the soil in which the moisture sensor is located.
Capacitance based moisture sensors generally operate by immersing two electrodes in soil, which forms a dielectric around the electrodes. The capacitance generated between the electrodes varies with the dielectric constant of the soil (which is known to vary with moisture content). However, known capacitance based sensors operate unreliably and are influenced by factors such as variations in temperature and supply voltage.